Amazonite
Encyclopedia
Amazonite is a green variety of microcline
feldspar
.
The name is taken from that of the Amazon River
, from which certain green stones were formerly obtained, but it is doubtful whether green feldspar
occurs in the Amazon area.
Amazonite is a mineral of limited occurrence. Formerly it was obtained almost exclusively from the area of Miass
in the Ilmen mountains, 50 miles southwest of Chelyabinsk
, Russia
, where it occurs in granitic rocks. More recently, high-quality crystals have been obtained from Pike's Peak
, Colorado
, where it is found associated with smoky quartz
, orthoclase
, and albite
in a coarse granite
or pegmatite
. Crystals of amazonite can also be found in Crystal Park, El Paso County, Colorado
. Some other localities in the United States
yield amazonite, and it is also found in pegmatite
in Madagascar
and in Brazil
.
Because of its bright green
colour when polished, amazonite is sometimes cut and used as a gemstone
, although it is easily fractured.
For many years, the source of amazonite's color was a mystery. Naturally, many people assumed the color was due to copper because copper
compounds often have blue and green colors. More recent studies suggest that the blue-green color results from small quantities of lead
and water in the feldspar. (Hoffmeister and Rossman, 1985)
Microcline
Microcline is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures...
feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
.
The name is taken from that of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
, from which certain green stones were formerly obtained, but it is doubtful whether green feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
occurs in the Amazon area.
Amazonite is a mineral of limited occurrence. Formerly it was obtained almost exclusively from the area of Miass
Miass
Miass is a city in Chelyabinsk Oblast, Russia, located west of Chelyabinsk, on the eastern slope of the southern Urals, on the bank of the Miass River. Population: -History:...
in the Ilmen mountains, 50 miles southwest of Chelyabinsk
Chelyabinsk
Chelyabinsk is a city and the administrative center of Chelyabinsk Oblast, Russia, located in the northwestern side of the oblast, south of Yekaterinburg, just to the east of the Ural Mountains, on the Miass River. Population: -History:...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, where it occurs in granitic rocks. More recently, high-quality crystals have been obtained from Pike's Peak
Pikes Peak
Pikes Peak is a mountain in the Front Range of the Rocky Mountains, west of Colorado Springs, Colorado, in El Paso County in the United States of America....
, Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
, where it is found associated with smoky quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, orthoclase
Orthoclase
Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...
, and albite
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
in a coarse granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
or pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
. Crystals of amazonite can also be found in Crystal Park, El Paso County, Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
. Some other localities in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
yield amazonite, and it is also found in pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
.
Because of its bright green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
colour when polished, amazonite is sometimes cut and used as a gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
, although it is easily fractured.
For many years, the source of amazonite's color was a mystery. Naturally, many people assumed the color was due to copper because copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
compounds often have blue and green colors. More recent studies suggest that the blue-green color results from small quantities of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and water in the feldspar. (Hoffmeister and Rossman, 1985)